Promote performance knowledge from community to Microsoft layer

Pure git-mv relocation of all 7 performance articles from community/knowledge/performance/ to microsoft/knowledge/performance/. No content changes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

microsoft/knowledge/performance/avoid-growing-globals-in-singleinstance-subscribers.md

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+---
+bc-version: [all]
+domain: performance
+keywords: [singleinstance, subscriber, event, memory, session]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Avoid growing globals in SingleInstance subscribers
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+A codeunit with `SingleInstance = true` is allocated once per session and lives until the session ends. Global variables on it are never collected between event fires. A subscriber that accumulates data into a global — buffering payloads, appending to a list, caching without a cap — steadily grows its session footprint for the entire user session. The symptom is memory that only recovers on sign-out, and it surfaces only on long-running sessions.
+
+## Best Practice
+
+Keep the global footprint on a SingleInstance subscriber bounded and intentional: a handful of flags, a setup record, a bounded cache with a maximum size. When cross-event state is genuinely needed, define an explicit reset point — end of a business process, arrival of a specific terminal event — that clears the growing collection.
+
+See sample: `avoid-growing-globals-in-singleinstance-subscribers.good.al`.
+
+## Anti Pattern
+
+A SingleInstance subscriber that appends each event's payload to a global list, dictionary, or temporary record without a cap or cleanup trigger. The list grows for hours, memory pressure builds quietly, and debugging the root cause on a live environment is substantially harder than noticing the unbounded append in code review.
+
+See sample: `avoid-growing-globals-in-singleinstance-subscribers.bad.al`.